package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.IndexReader;
import java.util.BitSet;
import java.util.WeakHashMap;
import java.util.Map;
import java.io.IOException;

/**
 * Wraps another filter's result and caches it. The purpose is to allow filters
 * to simply filter, and then wrap with this class to add caching.
 */
public class CachingWrapperFilter extends Filter {
	protected Filter filter;

	/**
	 * A transient Filter cache. To cache Filters even when using
	 * {@link RemoteSearchable} use {@link RemoteCachingWrapperFilter} instead.
	 */
	protected transient Map cache;

	/**
	 * @param filter
	 *            Filter to cache results of
	 */
	public CachingWrapperFilter(Filter filter) {
		this.filter = filter;
	}

	public BitSet bits(IndexReader reader) throws IOException {
		if (cache == null) {
			cache = new WeakHashMap();
		}

		synchronized (cache) { // check cache
			BitSet cached = (BitSet) cache.get(reader);
			if (cached != null) {
				return cached;
			}
		}

		final BitSet bits = filter.bits(reader);

		synchronized (cache) { // update cache
			cache.put(reader, bits);
		}

		return bits;
	}

	public String toString() {
		return "CachingWrapperFilter(" + filter + ")";
	}

	public boolean equals(Object o) {
		if (!(o instanceof CachingWrapperFilter))
			return false;
		return this.filter.equals(((CachingWrapperFilter) o).filter);
	}

	public int hashCode() {
		return filter.hashCode() ^ 0x1117BF25;
	}
}
